Alain Saliot

Hydrocarbons in surface sediments from the Changjiang (Yangtze River) Estuary, East China Sea

Sedimentary aliphatic (AH) and polycyclic aromatic hydrocarbons (PAHs) were studied in the Changjiang Estuary and the adjacent East China Sea. Total AH ranged from 2.20 to 11.82 microg g(-1) and consisted of n-alkanes and a dominant petroleum-related unresolved complex mixture (UCM). Within the n-alkanes, terrestrial plant wax compounds prevailed at nearly all stations. Of the PAHs, biogenic perylene dominated at stations receiving riverine inputs. Anthropogenic PAHs originating from combustion/pyrolysis processes varied from 17 to 157 ng g(-1), while fossil PAH concentrations ranged from 42 to 187 ng g(-1). Both biogenic and anthropogenic hydrocarbons are primarily derived from riverine discharges and accumulate at shallow-water stations. Distinct phase associations lead, nevertheless, to different sedimentation patterns. Fossil PAHs are enhanced at offshore stations where they are introduced directly by shipping activities. Biomarker fingerprints ascribe their source to Chinese crude oils. The overall levels of anthropogenic hydrocarbons are low compared to relevant areas worldwide and reveal a low/moderate level of hydrocarbon pollution.

Evolutionary trends in the lipid biomarker approach for investigating the biogeochemistry of organic matter in the marine environment

Abstract The detailed investigation of organic carbon cycling in estuarine and marine environments has stimulated the development of multidisciplinary concepts, research and sampling strategies as well as analytical tools in the last 10 years. Among other approaches, the molecular biomarker one has also undergone significant improvements. Some examples dealing with specific markers including sterols, alkenes and fatty acids are discussed in this paper in terms of source identification and transformation processes. Although some limitations exist for the elucidation of their stereochemistry, sterols have been used extensively to study biochemical processes affecting the organic matter in the water column and at the ocean/sediment interface. Sterols also appear as promising tracers of terrestrial vs. marine inputs in complex estuarine systems. The specificity of individual fatty acids or groups of acids has also been used to assess the origins and transformation processes of organic matter in marine samples. New approaches are presented including the investigation of intact lipid classes and the elucidation of the position of double bonds of unsaturated fatty acids and alkenes. Finally, we discuss the use of che-mometric techniques due to increasing chemical information and the interest of combining molecular-level and stable isotope approaches.

Refractory organic matter in sediments from the North–West African upwelling system: abundance, chemical structure and origin

Abstract Refractory (insoluble and nonhydrolyzable) organic matter (ROM) was studied in sediments underlying the north–west African upwelling system. Two core samples: beginning of glacial isotope stage 4 (ca. 70,000 yr BP; depth bsf 360 cm) and interglacial isotope substage 5d (ca. 90,000 yr BP; depth bsf 480 cm) were analyzed, along with a surface sample. ROM, which accounts for a substantial part of the total organic matter (OM) in these sediments (ca. 20% for the two core samples and 10% for the surface sample), was isolated and examined for its morphological and chemical features using a combination of transmission and scanning electron microscopy, spectroscopy (FTIR, solid state 13 C NMR) and analytical pyrolysis (Curie point flash pyrolysis–GC–MS). These studies allowed the chemical structure of the three ROMs (chiefly based on melanoidin-type macromolecules) and their mechanism of formation (degradation–recondensation of products mainly derived from proteinaceous material) to be established. Such a formation probably began in the water column and continued within the sediment upper layers. Important differences, concerned both with OM chemical structure and preservation mechanism, were noted upon comparison with recently studied sediments underlying the Peru upwelling system. These differences between the two systems, in spite of similarities in primary production, must reflect the combined influence of factors such as upwelling intensity (primary productivity), water depth and iron supply.

Organic matter sources and early diagenetic alterations in Arctic surface sediments (Lena River delta and Laptev Sea, Eastern Siberia)—I. Analysis of the carboxylic acids released via sequential treatments

Abstract The acid moieties occurring in marine, arctic, and surface sediments from the Lena River delta and adjacent Laptev Sea were analyzed by sequential treatments. Five acid fractions, corresponding to distinct pools, were thus obtained from each sample: the unbound acids (isolated from extracts), the OH − -labile acids (released by a classical saponification on the insoluble residue), the OH − (PTC)-labile acids (obtained via an additional saponification with a phase transfer catalyst), the H + -labile acids (released by a subsequent acid hydrolysis) and, finally, the tightly bound acids (only released by thermolysis). The existence of these different pools reflects differences in the mode of occurrence of the acids and/or in the protection provided by the (macro)molecular structures which they are linked to. To the best of our knowledge this study is the first example of a complete quantitative and qualitative analysis of acid moieties in recent sediment samples. Information was thus derived on (i) the relative importance of microalgal, bacterial and terrestrial contributions and the types of organisms implicated, (ii) the extent of early diagenetic alterations, (iii) the variations in the above features depending on the considered sample and pool and (iv) the mechanism of OM preservation and the control of TOC values and total fatty acids contents in such surficial sediments.

Origin and formation pathways of kerogen-like organic matter in recent sediments off the Danube delta (northwestern Black Sea)

The chemical structure, source(s), and formation pathway(s) of kerogen-like organic matter (KL) were investigated in recent sediments from the northwestern Black Sea, oA the Danube delta. Three sections from a sediment core collected at the mouth of the Sulina branch of the delta, under an oxic water column, were examined: S0 (0‐0.5 cm bsf), S10 (10‐13 cm bsf), and S20 (20‐25 cm bsf). The bulk geochemical features of these sediments (total organic carbon, organic C/N atomic ratio, d 13 Corg) were determined. Thereafter, KL was isolated from the samples, as the insoluble residue obtained after HF/HCl treatment. KL chemical composition was investigated via spectroscopic (FTIR, solid state 13 C and 15 N NMR) and pyrolytic (Curie point pyrolysis‐gas chromatography‐mass spectrometry) methods, and the morphological features were examined by scanning and transmission electron microscopy. Similar morphological features and chemical composition were observed for the three KLs and they suggested that the selective preservation of land-plant derived material as well as of resistant aliphatic biomacromolecules (probably derived from cell walls of freshwater microalgae) was the main process involved in KL formation. Besides, some melanoidin-type macromolecules (formed via the degradation-recondensation of products mainly derived from proteinaceous material) and/or some encapsulated proteins also contributed to the KL chemical structure. # 2000 Elsevier Science Ltd. All rights reserved.

Sources and transport of hydrocarbons in the Rhone delta sediments (Northwestern Mediterranean)

SummaryTo assess sources and transport processes of hydrocarbons in the Rhone delta, superficial sediments were collected near the river mouth and at the limit of the continental shelf in February 85 and September 86. After spiking with perdeuterated standards and isolation of lipids, a normal-phase HPLC step permitted the separation of hydrocarbons in non-aromatics (NAH) and aromatics (PAH), and the fractionation of the latter into sub-groups as a function of the number of aromatic cycles. Analysis of fractions and quantitation of individual compounds were performed by GC and GC/MS. Hydrocarbon concentrations varied from 21.2 to 166.7 μg/g for the NAH, and from 1070 to 6363 ng/g for the PAH. Relevant seasonal variations were observed, reflecting quantitative and qualitative fluctuations of inputs. Petrogenic, pyrolytic and natural derived imprints, as well as their respective contributions were evidenced by distribution patterns, values of ratios of characteristic compounds and occurrence of specific components. Pyrolytic inputs were considerably higher in winter, reflecting intense inputs from combustion processes and/or run-off. On the contrary, fossil as well as natural inputs were significantly higher in summer.

A geochemical investigation of carboxylic acids released via sequential treatments of two surficial sediments from the Changjiang delta and East China Sea

Two surface sediments from the delta of the Changjiang River (the fourth largest river in the world in terms of water discharge and the seventh in terms of sediment discharge) and an adjacent area of the East China Sea were subjected to sequential treatments in order to obtain complete, quantitative and qualitative, information on carboxylic acid moieties. Five successive treatments allowed for the release of all acid moieties occurring in each sample: (i) the ‘‘unbound’’ acids isolated from extracts, (ii) the OH ˇ -labile acids released by classical saponification, (iii) the OH ˇ (PTC)-labile acids obtained via an additional saponification with a phase transfer catalyst, (iv) the H + -labile acids released by a subsequent acid hydrolysis and (v) the tightly bound acids only released by thermolysis. These five fractions correspond to distinct pools whose occurrence reflects diAerences in the mode of linkage of the acid moieties and/or in the protection provided by the structures to which they are linked. Such analysis of acid moieties provided information on (i) the relative contributions from microalgae, bacteria and higher plants in the ‘‘delta’’ and ‘‘seaward’’ stations, (ii) the degree of early diagenetic alteration for the acids derived from these diAerent sources and (iii) the types of microalgal and bacterial species implicated. These features were also compared with the results of the only previous study where the sequential treatments were applied, on surficial sediments from a sharply diAerent environment (the Lena River delta, Arctic). # 2000 Elsevier Science Ltd. All rights reserved.

Thermally assisted hydrolysis and methylation of kerogen-like organic matter in a recent sediment off the Danube delta (northwestern Black Sea)

The kerogen-like organic matter (KL) isolated from the surface section of a recent sediment core off the Danube delta was analysed by flash pyrolysis in the presence of tetramethylammonium hydroxide (TMAH). The main compounds released from KL were lignin-derived phenols arising from the cleavage of the β-O-4 ether bonds. Aromatic units — methyl esters of benzenecarboxylic acids — occurred in major amounts and corresponded to cinnamyl, guaiacyl and syringyl units. The thermal degradation products also consisted of aliphatic series such as methyl esters of C5–C30 fatty acids, branched aliphatic acids, and α,ω-alkanoic diacids. Several nitrogen-containing compounds identified as both nitrogenous heterocycles and methylated amino acids were detected in the TMAH thermochemolysate. These results are compared to those of conventional flash pyrolysis previously performed, and the important qualitative and quantitative differences thus noted are discussed along with additional information on the chemical structure of KL and sources derived from thermally assisted hydrolysis and methylation (THM) with TMAH.

Phenylurea and triazine herbicides in the Garonne River (France) during high flood and low water periods

Abstract Phenylureas and triazines were analysed by reversed-phase liquid chromatography using UV detection at 254 nm after an on-line preconcentration step on a PRP-1 copolymer in order to determine pesticides in river water at μg/1 level or lower. Running water was sampled in the Garonne from a station located at La Reole, upstream from Bordeaux and from a small tributary, the Dropt. Water samples were collected mainly at several periods between December 1989 and September 1990 at a low water time (December 1989) and during two high flood periods (February 1990 and May 1990). Atrazine, simazine, de-ethylatiazine, diuron, chlortoluron and isoproturon were detected and quantified. In the Garonne river, atrazine, simazine, de-ethylatrazine and diuron were usually present at the sampling time, whereas chlortoluron and isoproturon maximised during the winter flood (February). In the Dropt river, triazine concentrations were normally between 1.0 and 0.1 μg/1 and maximised at 2.2 μg/1 during the spring flood (...

Winter distribution of algal pigments in small- and large-size particles in the northeastern Atlantic

Particles were collected by filtration on GF/F filters and by vertical hauls of 50 μm mesh-sized net throughout the water column (50–1700 m) in the northeastern Atlantic in January 1989 during the Medatlante t cruise, in the framework of the French JGOFS program. Particles were analysed for their organic carbon and algal chlorophyll and carotenoid pigments by high-performance liquid chromatography coupled with UV absorbance and fluorescence detection. Complementary analyses were performed on a surface sample for sterols and fatty acids by gas chromatography and gas chromatography/mass spectrometry. Organic carbon concentrations were 2–3 orders of magnitude higher in GF/F (10–50 μg l−1) than in net particles (0.01−0.06μg l−1). The same ratio was encountered for pigments: 4–603 ng l−1 and 0.003−0.037 ng l1¯, respectively. Among 11 GF/F samples collected between 500 and 1700 m, four samples contained pigments in detectable amounts (4–106 ng l−1). Their pigment distribution pattern was close to deep GF/F samples, but differed from the pigment pattern of deep net-collected particles, mainly composed of fecal pellets. This latter sinking material was enriched in chlorophyll degradation pigments and showed higher values of the ratio (sum of carotenoids)/(sum of chlorophylls) than those observed in small-size particles. The combined information from pigments, sterols and fatty acids shows that Prymnesiophytes in a post bloom situation contributed to a major part of the surface autotrophs. Two processes of rapid transfer of organic matter between the surface and the deep Mediterranean water are discussed: fecal pellets of herbivorous plankton and sedimentation of aggregates partly linked to the presence of Prymnesiophytes.